I firmly believe that documentaries are best approached in a state of blissful ignorance, and it was in such a condition that I encountered Jason Becker: Not Dead Yet.
Frankly, I had never heard of Becker, a flamboyant rock guitarist who gained a reputation as a coming talent in the late 1980s, recorded an album with David Lee Roth, then disappeared without a trace.
Jesse Vile's film about him opens with archive footage showing a young Becker preening about in leather trousers and dutifully shaking rock-guitarist hair.
It all seems pretty inconsequential, in fact, until you realise what happened to Becker next. Born in Richmond, California, Jason showed a precocious talent for music, and by the age of 12 was playing everything from Bach to Eric Clapton on an acoustic guitar.
He entered talent contests and played at high school shows, and at 16 he formed a band called Cacophony with future Megadeath guitarist Marty Friedman.
They released two albums that were well received, and soon Jason was being talked about as the next big American rock guitarist. The call to join David Lee Roth's band seemed to confirm that Becker was bound for greatness. But fate had other ideas.
In 1989, as he was preparing to go on tour with Roth, Becker began experiencing weakness and cramps in his legs. He assumed the cramps would pass, and didn't know he was experiencing the early stage of motor neuron disease, or Lou Gehrig's disease as it's called in the United States.
It's a singularly vicious ailment, that attacks the nervous system, atrophies muscles, and removes the sufferer's faculties one by one. Jason was given three years to live, and his parents and siblings prepared themselves for the worst.
But Becker didn't die. He did lose the power in his limbs, was confined to a wheelchair, lost his voice and, perhaps worst of all, the solace of playing guitar. But he battled on, and has become a hero for other sufferers of motor neuron disease.
Jesse Vile's documentary is very much a game of two halves: in the early sequences we see Becker young, cocky, perhaps a little indulged by his parents and full of the joys of life.
He might have become another loud and brassy 80s glam rocker, but his reaction to contracting this nightmarish disease has revealed extraordinary depth of character.
Helped by his parents and a saintly ex-girlfriend, Becker has slowly rebuilt his life and learnt to live with what for most of us would seem like a living death.
What's most striking about Becker is his complete lack of self-pity or bitterness. "I think I am lucky," he says at one point.
I'm not sure I agree with him.
Director: Jesse Vile Stars: Jason Becker, Serrana Pilar, Marty Friedman, Joe Satriani